title: Shear stiffness in nanolaminar Ti3SiC2 challenges ab initio calculations.
abstract: Nanolaminates such as the M(n + 1)AX(n) (MAX) phases are a material class with ab initio derived elasticity tensors published for over 250 compounds. We have for the first time experimentally determined the full elasticity tensor of the archetype MAX phase, Ti(3)SiC(2), using polycrystalline samples and in situ neutron diffraction. The experimental elastic constants show extreme shear stiffness, with c(44) more than five times greater than expected for an isotropic material. Such shear stiffness is quite rare in hexagonal materials and strongly contradicts the predictions of all published MAX phase elastic constants derived from ab initio calculations. It is concluded that second order properties such as elastic moduli derived from ab initio calculations require careful experimental verification. The diffraction technique used currently provides the only method of verification for the elasticity tensor for the majority of new materials where single crystals are not available.
authors.affiliation: School of Engineering, University of Newcastle, NSW 2308, Australia.
authors.forename: E H
authors.initials: EH
authors.lastname: Kisi
authors.forename: J F
authors.initials: JF
authors.lastname: Zhang
authors.forename: O
authors.initials: O
authors.lastname: Kirstein
authors.forename: D P
authors.initials: DP
authors.lastname: Riley
authors.forename: M J
authors.initials: MJ
authors.lastname: Styles
authors.forename: A M
authors.initials: AM
authors.lastname: Paradowska